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The Tubulous Boiler.


termed headers, which fit closely together. Every header is
connected, by a tube a, with a collecting chamber b at each end
of the receiver G; and all the tubes are expanded into their
respective sockets, the necessary holes at d being closed by
covers of ' mudhole' pattern. The water rises to the centre of
the receiver, which therefore serves both as dome and part of the
boiler. There is a cleaning hole at e. j is a cylindrical mud
collector, while K, L, M, and N are soot doors; and the draught
is compelled to follow the tubes, by reason of the division
walls c and D, the flame plates Q Q, and the position of flue E.
The receiver is held in place by the girders p P, bolted to
the brickwork. The headers are usually of cast iron, though
wrought-iron ones have been recently constructed, and plates Q Q,
with firebrick distance pieces, serve to stay and support the tubes
intermediately. The chambers b b are flanged and welded from
wrought-iron plate, the tubes are of wrought iron or steel, and the
receiver of steel plate. The flue may be at N instead of E.

These boilers have been much favoured recently by electric-
lighting engineers, on account of rapid steam-raising properties,
and immunity from accidents due to the small diameter of their
tubes, with relatively great strength; but they require considerable
cleaning and repairing. (See Appendices, pp. 828, 993, and 1061.)

Geometry required by the Boiler Maker.—This is not
of a difficult kind, but involves one or two intersections of solids,
and development of the contact line upon either ,of the solids
when their surfaces are laid flat He must know the relation of
circumference to diameter of circle, thus—

Circumference =

and TT •

diameter x ?r
3-1416 or ~

and the diameter of a boiler should be measured (for develop-
ment) to the centre of thickness of the plate.

The intersection of cylinder with cylinder is given at Fig. 315,
and the method of developing the plane surface: A and B repre-
senting a dome and boiler respectively. Taking the dome in
plan, divide the-circle, into, say, twelve parts, an<3 nwnber ;as
shewn. Calculate half-dome circumference, and lay out as at
CD, dividing into six parts by vertical lines. Project lines up